Field of the Invention
Railway tracks for trains, trams, small gauge trains or large capacity dredger excavators are subject to wear and tear on curves or points and crossings as a result of lateral forces. Wear also occurs on the wheel flanges of the rail vehicles. In general, lubricants have been employed to protect rails, points and crossings and the wheel flanges of rail vehicles against this source of wear. The lubricant also serves to reduce the noise level emitted from these points.
A grease is normally employed to ameliorate the wear problems described above. The grease conventionally consists of a mineral lubricating oil as the main constituent as well as fatty acid soaps, especially calcium soaps, as thickening agents. Depending on requirements, such a grease composition will also contain small amounts of additional additives, such as anti-oxidants, anti-corrosion additives, extreme pressure additives and the like. In many cases, the conventional lubricating grease will also contain solid lubricants such as graphite or molybdenum disulphide. The composition and mode of action of known wheel flange lubricating greases is described in the Requirements Standard of the German Federal Railway, substance No. 077.02, January, 1974, and in "Standard Handbook of Lubrication Engineering," McGraw-Hill, 1968, chapter 43, pages 18-21.
A disadvantage of the known grease compositions for rails and rail vehicles is that they contain large amounts (in general 80-90%) of mineral lubricating oils. Mineral oils are not readily biodegradable. When using such a grease composition in the maintenance of railway tracks or trams, comparatively large amounts of the relatively non-degradable mineral oil component will pass into the sanitary sewage system as a result of rain or when the streets are cleaned by washing thus creating a serious contamination problem. Environmental harm also arises when the grease of optionally tracked rubbish excavators, or dredger excavators, cables, links and other similarly lubricated parts comes into direct contact with or contaminates the soil and/or surface waters.